Rotating wick device

ABSTRACT

A rotating wick device for applying release oil to a fusing roller or other fuser member includes an elongated hollow distribution tube. A porous ceramic material surrounds the distribution tube and is covered with a porous polytetrafluoroethylene material. Preferably, the polytetrafluoroethylene material includes a first portion adjacent the ceramic material which is of unexpanded polytetrafluoroethylene and a second portion adjacent the first portion which is expanded polytetrafluoroethylene.

This invention relates to apparatus for fusing toner images and, moreparticularly, it relates to a rotating wick device for applying offsetpreventing liquid to a surface of a fusing apparatus.

U.S. Pat. No. 4,229,990, granted to E. J. Tamary Feb. 7, 1984, disclosesa wicking structure for applying release liquid to the surface of aroller in a roller fixing apparatus. Such release liquid (sometimesreferred to as "oil") is fed from a reservoir to a replaceable porousapplicating wick. The feed tube and wick constitute an applicationroller which is rotated by the fusing or fixing roller while it oils thesurface. The structure has many advantages, including ease inarticulation and low wear on the surface being oiled.

The structure shown in that patent is commonly called a "rotating wick"and is presently used commercially in a number of copiers and printersapplying high quantities of oil to rollers for 250,000 or more imagesper wick. The release liquid is delivered to the wick using a pump and arotatable or stationary feed tube. The feed tube is cylindrical and hassmall holes through which the liquid can pass. A replaceable wicksurrounds the feed tube which includes a porous structure having aninner ceramic porous material that is covered by a porous and heatresistant fabric such as wool or a comparable synthetic fabric. Such asynthetic fabric is marketed by DuPont under the trademark Nomex® and isa well known capillary fabric which is resistant to heat and used for avariety of fusing system wicks.

U.S. Pat. No. 4,908,670, issued Mar. 13, 1990, and U.S. Pat. No.3,964,431, are also internally fed wicking structures with variations inthe porous material used.

U.S. Pat. No. 5,043,768, granted to Baruch Aug. 27, 1991, shows arotating wick in which the wool or Nomex® wrap has been eliminated andthe porous ceramic material directly contacts the surface being oiled.This structure has been shown to have some advantages for some uses.Typical ceramic materials useful in this and in the Tamary wick werecomposed of aluminum oxide, silicon dioxide and other materials. Theyare generally off-the-shelf items that can be purchased from a supplierof such porous ceramics.

U.S. Pat. No. 5,232,499 to Kaitoh et al, issued Aug. 3, 1993, and UKPatent Application 2 261 400, are among several patent documents to W.L. Gore Associates, Inc. which show rotating wicks designed for applyingoil to a fixing surface in a plain paper copying machine. A porouspolytetrafluoroethylene structure is wrapped around a metal tube orporous foam through which release liquid moves from an internalreservoir without a pump. This structure applies liquid at a very slowrate and lasts only as long as the internal supply lasts.

Two problems associated with pumped (and not pumped) rotating wicks, aswell as other oil application devices, continue despite all of theadvantages of the above art. The first is the general uniformity of theoil applied, regardless of the conditions of use of the machine. Thesecond is the tendency of wicks to apply oil to areas of the fuser thatare not being used which can cause a buildup of oil. This latter problemis especially present in a fuser designed to take varying cross-tracklengths of substrate. If too little oil is applied to a fusing roll,release of the toner and substrate can degrade to the point where copyjams occur in the fuser or part of the toner image sticks to the fuserroll instead of the substrate. If too much oil is applied to the fuserroll, visual oil stains can occur on the substrate, especially if thesubstrate is paper.

SUMMARY OF THE INVENTION

It is an object of the invention to improve on the performance of priorrotating wick oil applying devices.

This and other objects are accomplished by a rotating wick device forapplying offset preventing oil to a surface in a fuser, the oil applyingdevice including: a) a distribution device through which oil can flow;b) a porous ceramic material surrounding the device; c) and a porousmaterial comprising porous polytetrafluoroethylene (PTFE) around theouter surface of the ceramic material.

According to a preferred embodiment, the polytetrafluoroethylenematerial is made up of two portions, an inner portion directlycontacting the ceramic material, which inner portion is an unexpandedporous polytetrafluoroethylene, preferably wrapped on the ceramicmaterial and a second portion which is a porous expandedpolytetrafluoroethylene material, preferably in the form of a sleeveover the unexpanded polytetrafluoroethylene wrap.

Surprisingly, we found that use of the polytetrafluoroethylene materialssimilar to those suggested in the above-cited W. L. Gore Associates,Inc. disclosures, when applied to a prior ceramic core, provided betteroverall consistency of oil application, including application whenfusing varying cross-track lengths of substrate, than did the otherwicks used as suggested in the prior art. This improvement was true evenin a high oil lay-down environment with oil pumped to the wick from areservoir.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic side section of a rotating wick contacting asurface to be oiled.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the FIGURE, a surface 1, for example a fusing rollersurface, is to be oiled. The surface is moving and frictionally rotatesa wick 10 which is supported about an axis primarily by a usuallynon-rotatable distribution tube 12 and other known components at theends of the wick 10, not shown. A pump 24 feeds oil from a reservoir 30into the distribution tube 12, which liquid exits the distribution tubethrough small holes, not shown. Coaxial with the distribution tube 12 isthe replaceable wick 10 which includes a cylindrical porous ceramicmaterial 14, airspaced from the distribution tube 12. The porous ceramicmaterial 14 can be the same as that presently in commercial use. Suchstructures can be predominantly aluminum oxide or silicone dioxide andgenerally include some other material. They are purchased as anoff-the-shelf item from a supplier of such materials.

The ceramic material 14 was covered with two materials supplied by W. L.Gore Associates, Inc. The first material 16 is a porous, unexpanded PTFEand was wrapped directly onto the ceramic material for two or threewraps. The second material 18 was a porous expanded PTFE material andwas applied as a sleeve 20 over the wrapped unexpanded PTFE.

The ceramic material 14 and the PTFE covering make up the wick 10 whichis replaceable over the distribution tube and rotates with respect toit.

Relatively rigorous tests were run with 1) the wick just described, 2) awick with just the ceramic material directly contacting the fusingroller surface, similar to that described in U.S. Pat. No. 5,043,768, 3)a wick as presently in commercial use in which the same ceramic materialis covered with Nomex®, and 4) a wick supplied by W. L. Gore Associates,Inc. and having the same PTFE covering as in wick 1) over a widediameter metal distribution tube.

All four wicks were tried under three different conditions. The firstcondition included fusing larger substrates after varying length runs ofsmaller substrates. The second condition was a long copy run after anovernight (greater than 15 hour) period of nonuse. The third conditionwas a long copy run after 90 minutes of nonuse.

The uncovered porous ceramic core (wick 2), while applying uniform oilin short runs, applied undesirably low amounts of oil during the middleof the long runs.

The standard wick (wick 3) had difficulty handling the situation inwhich larger copies were run after long runs of smaller copies. Thebuildup of oil outside the smaller copy area had a tendency to stain thelarger copies.

The metal tube porous PTFE wick (wick 4) stained copies after the longnonuse periods.

The wick fabricated according to the invention with the PTFE coveringthe ceramic material actually performed better than any of the otherwicks. It applied less oil to the fuser roll directly when smallersubstrates were run than did the standard wick. It applied less oilafter long periods of nonuse than did the porous PTFE metal core wick,and it more consistently delivered sufficient amounts of release oilthan did the uncovered ceramic wick.

In the above example, the ceramic material was separated from thedistribution tube by about 2 mm. However, in conditions where excessoiling after rest is a problem, much smaller airspaces work better, forexample, airspaces less than 1 mm, with an airspace as small as 0.3 mmbeing particularly effective in this respect.

The invention has been described in detail with particular reference toa preferred embodiment thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described hereinabove and as defined in the appendedclaims.

We claim:
 1. A rotating wick device for use in applying offsetpreventing oil to a surface in a fuser, said device including:adistribution device through which oil can flow, a porous ceramicmaterial surrounding said distribution device, and a porouspolytetrafluoroethylene material surrounding the ceramic material, saidpolytetrafluoroethylene material including two portions, an innerportion contacting the ceramic material which includes a porousunexpanded polytetrafluoroethylene material and an outer portioncontacting the inner portion which includes an expandedpolytetrafluoroethylene material, at least the ceramic material and thepolytetrafluoroethylene material being rotatable by the surface beingoiled.
 2. A rotating wick device according to claim 1 wherein the innerportion is wrapped on the ceramic material and the outer portion is asleeve over the inner portion.
 3. A rotating wick device according toclaim 1 wherein the distribution device is a non-rotatable elongatedhollow distribution tube having a plurality of holes through which oilunder pressure can flow.
 4. A rotating wick device according to claim 3further including a reservoir of oil and a pump for delivering oil fromthe reservoir to the distribution tube.
 5. A rotating wick deviceaccording to claim 3 wherein the ceramic material is separated from thedistribution tube by an airspace of less than 1 mm.
 6. A rotating wickdevice according to claim 5 wherein the airspace is about 0.3 mm.
 7. Awick for use in a rotating wick device for applying oil to a surface ina fuser, which rotating wick device has a distribution device throughwhich oil can flow, said wick comprising:a porous ceramic materialpositionable over said distribution device, and apolytetrafluoroethylene material surrounding the ceramic material, saidpolytetrafluoroethylene material including two portions, an innerportion contacting the ceramic material which includes a porousunexpanded polytetrafluoroethylene material and an outer portioncontacting the inner portion which includes an expandedpolytetrafluoroethylene material.